How Do We Hear?

There are three parts to the ear: the outer ear, the middle ear and the inner ear. Each part has special functions and can be affected by specific diseases that cause different symptoms and problems.

The outer ear

The outer ear has two major parts, the pinna and the external auditory canal. The pinna is that part of the ear that protrudes from the side of the head and is clearly visible when we look at someone. The pinna is the part of the ear with which we are all familiar. The function of the pinna is to collect sounds and funnel them towards the organ of hearing deep within the head. The external auditory canal is the channel that carries the sound collected by the pinna to the ear drum (tympanic membrane).

The middle ear

The middle ear is bounded on one side by the ear drum and on the other by the inner ear. The function of the middle ear is to take the sound collected by the outer ear and concentrate and direct that sound to the inner ear. As the sounds collected by the outer ear strike the ear drum the ear drum vibrates (like the top of a musical drum). There are three little bones in the middle ear that act as a lever mechanism and direct the sound energy from the vibrating ear drum to the inner ear. The first bone of hearing, attached to the ear drum, is called the malleus. The middle bone of hearing is called the incus. The smallest bone in the human body, and the one that presents sound to the inner ear, is called the stapes. These three bones act as a lever mechanism and transmit sound from the ear drum to the inner ear.

The inner ear

The inner ear has two key components, the organ of hearing and the organ of balance. The organ of hearing is called the cochlea. The cochlea contains fluid and little cells, called “hair cells.” These cells are called hair cells because there are tiny “hairs” on the top of these cells that float in the fluid of the inner ear. Each of the hair cells connects to a branch of the nerve of hearing that goes from the inner ear to the brain.

The stapes bone sits in a window that separates the middle ear from the inner ear, called the oval window. When the stapes bone moves, the fluid of the inner ear moves and the little hairs on top of the hair cells bend. When these hairs bend the mechanical energy coming from the outer ear and middle ear is converted into an electrical signal that travels up the nerve of hearing to the brain, where we perceive sound and speech.

The organ of balance is called the labyrinth. There are hair cells in the labyrinth that are similar to those in the organ of hearing. When we move these hairs bend and we perceive motion. When we turn, we are aware that we are turning because the inner ear is being stimulated. When we go up in an elevator, we sense that we are going up because the inner ear is being stimulated. Vertigo is defined as the false sensation of motion that often happens when the inner ear malfunctions.